Radio communication apparatus using adaptive antenna

ABSTRACT

In a radio communication apparatus, delay profiles of a desired wave and delay waves thereof are estimated by plural delay profile estimation sections for each of received signals from directional antennas constituting an array antenna. Received signals from the antennas selected by a reception antenna selector on the basis of the delay profile are subjected to a temporal/spatial equalization processing by an adaptive signal processing section and a path diversity combining section, thereby obtaining a reception output. An arrival angle range of the desired wave is estimated by a DOA estimation section from the delay profile estimated by the delay profile estimation section. Based on the arrival angle range, the antenna for transmission is selected by a transmission antenna selection section, and transmission signals are sent out.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is based upon and claims the benefit of priorityfrom the prior Japanese Patent Applications No. 11-371762, filed Dec.27, 1999; and No. 2000-351612, filed Nov. 17, 2000, the entire contentsof which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

[0002] The present invention relates generally to a radio communicationapparatus using an adaptive antenna, which is applied to a mobile radiocommunication system, etc., and more particularly to a transmission beamcontrol apparatus for desirably controlling antenna directivity at thetime of transmission.

[0003] In land mobile communications, there will frequently occurdegradation in received signal level due to fading, or a signaldistortion due to co-channel interference (CCI) or intersymbolinterference (ISI).

[0004] In such a severe environment for signal propagation, in order toexactly extract a desired wave, it is effective to use an adaptiveantenna which suitably controls antenna directivity. Adaptive arrays arewell-known as an example of adaptive antennas. Adaptive arrayspossibility suppress interface signals by pointing nulls to interfacingstations.

[0005] In land mobile communications, however, the size of a terminalstation needs to be reduced for portability. In general cases, adaptivearrays are applied to a base station because of having plural antennas.

[0006] Adaptive arrays are array antennas which synthesize receivedsignals from a plurality of antennas by controlling the phases andamplitudes of the signals. Even when high-level interference waves arepresent, a beam is turned to a direction from which a desired wave isincident and nulls (a point with no gain) are turned to directions fromwhich interference waves are incident. Thereby, a reception SIR (adesired wave to interference wave ratio) can be increased to a maximum.

[0007] The operation of controlling and synthesizing the phases andamplitudes of received signals is equivalent to an operation whereinreceived signals from plural antennas #1, #2, . . . , #N are subjectedto complex weighting, as shown in FIG. 1, by means of complexmultipliers 1-1, 1-2, . . . , 1-N, which multiply N received signals byreception weight vectors calculated by a reception weight vectorcalculation section 2, and the resultant signals are synthesized by anadder 3. In this case, an output y (“adaptive array output”) from theadder 3 is given by

y=w ^(T) x  (1)

[0008] In this equation, w is a complex weight vector (hereinafterreferred to as “reception weight vector”) applied to the received signalfrom each antenna, and x is a complex received signal vector from eachantenna, w and x being expressed by

w=(w1, w2, . . . , wj, . . . , wN)^(T)  (2)

x=(x1, x2, . . . ,xj, . . . ,xN)^(T)  (3)

[0009] wherein T denotes transposition of matrix.

[0010] The reception weight vector w is controlled so that the adaptivearray output y may satisfy a predetermined criterion. According tocriteria, for example, an average square error between the adaptivearray output y and an ideal signal sequence is reduced to a minimum, ora signal power of the adaptive array output y is reduced to a minimumunder a constraint on the direction of arrival (DOA) of a desired wave.In this way, with respect to the reception in the base station (that isuplink), the received signals from plural antennas are weighted andconsequently a distortionless signal can be obtained.

[0011] The above description is directed to the case where aomni-directional antenna is used as antenna, and this type of signalprocessing is called “element space processing.” On the other hand,there is known “beam space processing” wherein a plurality of beams withdifferent directions of radiation are formed in advance and receivedsignals obtained by the beams are subjected to an adaptive arrayprocessing.

[0012] If a beam space adaptive array is used, a pre-processing beamgenerator needs to be additionally provided. However, since a signaloutput with a high SNR (signal-to-noise ratio), combined with a beamgain, is obtained, a stable adaptive array processing can be expected byselecting appropriate beams. Moreover, since the number of branchesinput to the adaptive array can be reduced, the amount of arithmeticoperations for signal processing can be reduced accordingly.

[0013] This feature is described, for example, in document [1] (Chiba,Nakajo, Fujise, “BEAM SPACE CMA ADAPTIVE ARRAY ANTENNA”, IEICETransaction of the Communications, B-II, vol. J77-B-II, no. 3, pp.130-138, March 1994).

[0014] In general, a beam space adaptive array generates spatiallyorthogonal beams. However, as non-orthogonal beams, an adaptive antennausing directional antennas overlapping between adjacent beams has beenstudied.

[0015] For example, document [2] (Jpn. Pat. Appln. KOKAI Publication No.10-256821 (Matsuoka, et al.)) proposes an adaptive antenna capable ofefficiently combining delay wave energy by performing not only a spacedomain process using an adaptive array antenna but also a time domainprocess using path diversity.

[0016] On the other hand, many downlink beam forming methods tosynthesis optimal transmission beam pattern using an array antenna hasbeen studied. For example, in TDD (Time Division Duplex) system whereintransmission/reception is periodically switched by time division, sincethe same frequency is used in the transmission/reception, it can beregarded that the propagation channel responses of transmission andreception are substantially equal.

[0017] Accordingly, as shown in document [3] (Tomisato, Matsumoto,“EFFECT OF ADAPTIVE TRANSMISSION ARRAY IN TDD MOBILE COMMUNICATIONSYSTEM”, 1997-IEICE Spring conference, B-5-87, March 1997), thereception SIR at the terminal station can be improved by using the sameweight vector for transmission/reception, i.e., by forming the sameantenna pattern in transmission as is obtained at the time of reception.

[0018] However, as in the case of FDD (Frequency Division Duplex) wheredifferent frequencies are used for transmission and reception, thecorrelation in propagation channel response between uplink and downlinkis small. Thus, even if a transmission weight vector that is equal to areception weight vector is used, optimal reception at the terminalstation is not always ensured (e.g. see document [4] (J. Litva, T. K.-Y.Lo, “Digital Beamforming in Wireless Communications,” Artech HousePublishers, pp. 182-183, 1996).

[0019] As stated above, although the propagation channel responsediffers between uplink and downlink, there is reversibility betweenuplink and downlink with respect to the direction of arrival of radiowaves. Specifically, except for a case where the speed of movement ofthe terminal station is excessively high, the reception SIR at theterminal station can be increased to a maximum by estimating DOA ofreception ratio waves at the base station and setting the beam and nullin that direction.

[0020] For the purpose of such transmission beam pattern control, theestimation of the DOA is indispensable. As a signal processing for theestimation of the DOA, there is known a MUSIC (MUltiple SIgnalClassification) algorithm, etc. are known.

[0021] However, a great amount of calculations is required for ahigh-resolution DOA estimation algorithm represented by MUSIC. Thisalgorithm is not suitable in a case of estimating the DOA which variesfrom time to time depending on the movement of the terminal station or avariation in environment.

[0022] Even if numerous arithmetic operations are performed to preciselyestimate the DOA, and the weighting for directivity is carried out toset the null in the estimated DOA, the direction of the null may deviatedue to defective calibration of the transmission circuit. Furthermore,the effect of this technique may deteriorate due to the angle spread byreflection/dispersion near the terminal station in the actualpropagation path. As a result, the average reception SIR at the terminalstation may deteriorate.

[0023] Besides, if the number of incoming waves is greater than thenumber of antennas in the multi-path environment, it is difficult toestimate the DOA by MUSIC.

[0024] The present invention has been made to solve the above problems,and its object is to provide a radio communication apparatus which isapplicable to a system using different frequencies for uplink anddownlink and can easily estimate a DOA of radio waves and enhance anaverage reception SIR at an opposing-side station.

BRIEF SUMMARY OF THE INVENTION

[0025] In order to solve the above problems, the present invention hasthe main feature that an arrival angle range indicating an approximatearrival direction of a desired wave is estimated on the basis of a delayprofile estimated in a reception system for a predetermined signalprocessing (e.g. a temporal/spatial equalization signal processing), andan optimal antenna or beam is selected on the basis of the arrival anglerange, thereby effecting signal transmission.

[0026] Specifically, a radio communication apparatus according to thepresent invention comprises: a plurality of antennas disposed in apredetermined shape and having different directivities; a plurality ofdelay profile estimation means each for estimating delay profilesrepresenting arrival times of a desired wave and delay waves andreceived powers for each of received signals from the antennas; arrivalangle range estimation means for estimating an arrival angle range ofthe desired wave from the estimated delay profiles; transmission antennaselection means for selecting at least one of the antennas which is tobe used for transmission, on the basis of the estimated arrival anglerange; and transmission means for effecting transmission using theselected antenna.

[0027] With the above structure, in a mobile radio communication systemusing different frequencies for uplink and downlink, an arrival anglerange of a desired wave can easily be estimated only by observing areceived power value of each of the desired wave and delay waves, makinguse of a delay profile for each directional antenna which has alreadybeen measured for a temporal/spatial equalization processing. It ispossible to easily select an optimal transmission antenna based on aradio wave arrival direction in which reversibility is establishedbetween uplink and downlink. An average reception SNR and an averagereception SIR can be enhanced at an opposing-side station. Since anarrival angle range can be detected for delay waves at the same time, atransmission (time) diversity effect is expected to be obtained by usingthe DOA for delay wave.

[0028] In the above basic structure, the radio communication apparatusmay further comprise arrival direction estimation means for estimating adirection of arrival of the desired wave from the arrival angle rangeestimated by the arrival angle range estimation means; and transmissionweight vector generating means for generating such transmission weightvectors as to set a maximum gain direction of directivity at a time oftransmission in the estimated arrival direction.

[0029] In this case, the transmission antenna selection means selects aplurality of antennas included in the arrival angle range estimated bythe arrival angle range estimation means, and the transmission meansfeeds to the antennas selected by the transmission antenna selectionmeans transmission signals multiplied by the transmission weight vectorsgenerated by the transmission weight vector generating means, andtransmits the transmission signals. Thereby, the maximum gain directionof the transmission beam can be made to coincide with the desired wavearrival direction, and the average reception SNR can be maximized at theopposing-side station.

[0030] Another radio communication apparatus according to the inventioncomprises: a plurality of antennas disposed in a predetermined shape;beam forming means, connected to each antenna, for forming a pluralityof beams having different directions of radiation; a plurality of delayprofile estimation means each for estimating delay profiles representingarrival times of a desired wave and delay waves and received powers foreach of received signals by the formed beams; arrival angle rangeestimation means for estimating an arrival angle range of the desiredwave from the estimated delay profiles; transmission beam selectionbeams for selecting at least one of the beams which is to be used fortransmission, on the basis of the estimated arrival angle range; andtransmission means for effecting transmission using the selected beam.

[0031] With this structure, like the above-describe one, an arrivalangle range of a desired wave can easily be estimated by making use of adelay profile. It is possible to easily select an optimal transmissionantenna based on a radio wave arrival direction in which reversibilityis established between uplink and downlink. An average reception SNR andan average reception SIR can be enhanced at an opposing-side station.

[0032] In this basic structure, the radio communication apparatus mayfurther comprise: arrival direction estimation means for estimating adirection of arrival of the desired wave from the arrival angle rangeestimated by the arrival angle range estimation means; and transmissionweight vector generating means for generating such transmission weightvectors as to set a maximum gain direction of directivity in theestimated arrival direction.

[0033] In this case, the transmission beam selection means selects aplurality of beams included in the arrival angle range estimated by thearrival angle range estimation means, and the transmission meansreflects on the beams selected by the transmission beam selection meanstransmission signals multiplied by the transmission weight vectorsgenerated by the transmission weight vector generating means, andtransmits the transmission signals. Thereby, the maximum gain directionof the transmission beam can be made to coincide with the desired wavearrival direction, and the average reception SNR and average receptionSIR can be maximized at the opposing-side station.

[0034] In an embodiment, in the arrival direction estimation means, thearrival direction is detected by performing a scan using a predeterminedscanning beam pattern within the arrival angle range estimated by thearrival angle range estimation means, and finding a maximum value of areception output level obtained by the scan. Thereby, it is possible toeasily estimate the arrival direction necessary for forming thetransmission beam pattern for effecting maximum-gain radiation in thedesired DOA.

[0035] In another embodiment of the arrival direction estimation means,the arrival direction is detected by performing a scan using apredetermined scanning null pattern within the arrival angle rangeestimated by the arrival angle range estimation means, and finding aminimum value of a reception output level obtained by the scan. Comparedto the scan using the scanning beam pattern, the desired wave arrivaldirection can be estimated more precisely.

[0036] In still another embodiment of the arrival direction estimationmeans, the above two means are combined, and the arrival direction isdetected by performing a scan using a predetermined scanning beampattern and a scan using a predetermined scanning null pattern withinthe arrival angle range estimated by the arrival angle range estimationmeans, and finding a maximum value in difference between receptionoutput levels obtained by the both scans. According to this method,compared to the arrival direction estimation method using only one ofthe beam pattern scanning and null pattern scanning, the error inestimation of the arrival direction can be reduced.

[0037] The transmission section may effect transmission by forming atransmission beam pattern which has a maximum gain in the arrivaldirection of the desired wave and has suppressed side lobes indirections other than the arrival direction of the desired wave. In thiscase, it is not always possible to maximize the average reception SIR atthe opposing-side station. However, the beam capable of achieving highSIR can be formed even in a case where the arrival direction ofinterference waves varies over time. Moreover, since there is no need touse the high-resolution arrival direction estimation method for the nullcontrol, the amount of arithmetic calculations can be remarkablyreduced.

[0038] Additional objects and advantages of the invention will be setforth in the description which follows, and in part will be obvious fromthe description, or may be learned by practice of the invention. Theobjects and advantages of the invention may be realized and obtained bymeans of the instrumentalities and combinations particularly pointed outhereinafter.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

[0039] The accompanying drawings, which are incorporated in andconstitute a part of the specification, illustrate presently preferredembodiments of the invention, and together with the general descriptiongiven above and the detailed description of the preferred embodimentsgiven below, serve to explain the principles of the invention.

[0040]FIG. 1 shows the structure of a conventional receiving adaptivearray antenna;

[0041]FIG. 2 is a block diagram showing the structure of a radiocommunication apparatus according to a first embodiment of the presentinvention;

[0042]FIG. 3 shows an example of states of arrival waves and delayprofiles;

[0043]FIG. 4 is a block diagram showing the structure of a radiocommunication apparatus according to a second embodiment of the presentinvention;

[0044]FIG. 5 is a block diagram showing the structure of a radiocommunication apparatus according to a third embodiment of the presentinvention;

[0045]FIG. 6 is a block diagram showing the structure of a radiocommunication apparatus according to a fourth embodiment of the presentinvention;

[0046]FIGS. 7A to 7F show states of estimation of the direction ofarrival (DOA) by a beam pattern scan and a null pattern scan accordingto a fifth embodiment of the invention;

[0047]FIG. 8 is a block diagram showing the structure of a DOAestimation section according to a sixth embodiment of the invention;

[0048]FIG. 9 is a block diagram showing the structure of a DOAestimation section according to a seventh embodiment of the invention;and

[0049]FIG. 10 is a block diagram showing the structure of a DOAestimation section according to an eighth embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0050] Embodiments of the present invention will now be described withreference to the accompanying drawings. In the following description,the radio communication apparatus of this invention is applied to a basestation of a mobile radio communication system. The present invention,however, is applicable to a terminal station of the system with the samestructure, and the same advantages are obtained. In the followingdescription, it is assumed that this invention is applied to an FDD(Frequency Division Duplex) system. However, this invention is alsoapplicable to a TDD (Time Division Duplex) system with the samestructure.

[0051] (First Embodiment)

[0052]FIG. 2 is a block diagram showing the structure of a radiocommunication apparatus according to a first embodiment of the presentinvention.

[0053] The radio communication apparatus of this embodiment comprises aplurality of antennas 10-1 to 10-N for transmission/reception, whichhave mutually different directivities; duplexers 11-11 to 11-N fordividing transmission/reception signals having different frequencies;delay profile estimation sections 12-1 to 12-N; a reception antennaselector 13 for selecting a predetermined number of antennas forreception (i.e. reception antennas) from the antennas 10-1 to 10-N; anadaptive signal processing section 14 and a path diversity combiner 15for subjecting the received signals from the selected reception antennasto a temporal/spatial equalization signal processing; a control section16 for controlling the reception antenna selector 13; a DOA (Directionof Arrival) estimation section (an arrival angle range estimationsection) 17 for estimating a range of angles of arrival of a desiredwave; a transmission antenna selector 18 for selecting one antenna fortransmission (transmission antenna) from the antennas 10-1 to 10-N; anda switch 19 for supplying a transmission signal to the selectedtransmission antenna.

[0054] [Re: Reception Operation]

[0055] A reception operation of the radio communication apparatus willnow be described. The antennas 10-1 to 10-N are disposed in apredetermined shape such as a circular shape. The antennas 10-1 to 10-Nreceive radio waves sent from opposing-side stations, that is, terminalstations, and output received signals. The received signals from theantennas 10-1 to 10-N are input to the reception antenna selector 13 viathe duplexers 11-1 to 11-N.

[0056] In parallel with this, the delay profile estimation sections 12-1to 12-N estimate delay profiles (average delay profiles) of associatedreceived signals. The average delay profile in this context meansmeasurement results of the arrival time and average received power of adesired wave and a delay wave thereof.

[0057] Each of the delay profile estimation sections 12-1 to 12-N isrealized by a sliding correlator, etc., and it can also be realized by amatched filter, etc. in a CDMA (Code Division Multiplex Access) system,etc. Since the frequency band is spread by spreading codes in the CDMA,the delay profile can be estimated by an inverse-number interval of achip rate. In addition, in a modulation/demodulation system wherein theeffect of filtering can be ignored, the temporal resolution can beenhanced by a sliding correlator in which taps are disposed at intervalsof fractions.

[0058] On the basis of the average delay profiles estimated by the delayprofile estimation sections 12-1 to 12-N, the reception antenna selector13 is controlled by the control section 16 so as to select optimalreception antennas for desired wave components with respective delaytimes. In the case of the structure of the present embodiment whereinthe temporal/spatial equalization processing is performed by theadaptive signal processing section 14 and path diversity combiner 15 atthe rear stage of the reception antenna selector 13, the delay wave canbe regarded as the desired wave which has traveled through differentpropagation paths.

[0059] In this way, the control signal from the control section 16enables the reception antenna selector 13 to select optimal receptionantennas for desired wave components with associated delay times. Thereceived signals from the selected reception antennas are subjected tothe spatial equalization processing, such as adaptive array processing,in the adaptive signal processing section 14, and then to the temporalequalization processing in the path diversity combiner 15.

[0060] The operations of the reception antenna selector 13, adaptivesignal processing section 14 and path diversity combiner 15 aredescribed in Jpn. Pat. Appln. KOKAI Publication No. 10-256821. Theseoperations may be summarized as follows.

[0061] The reception antenna selector 13 selects K (K<N) receptionantennas with higher received powers from N antennas 10-1 to 10-N fordesired wave components with respective delay times (for simplerdescription, assume three waves: (1) a direct wave with no delay, (2) a1-symbol delay wave and (3) a 2-symbol delay wave). The received signalsfrom the selected reception antennas are supplied to the adaptive signalprocessing section 14.

[0062] For example, with the same structure as shown in FIG. 1, theadaptive signal processing section 14 performs the spatial equalizationsignal processing by subjecting to a weighted addition processing eachreceived signal from the K reception antennas selected for the desiredwave components with associated delay times. The weight vectors used inthis case are so determined as to increase the desired wave component inthe received signals and to suppress other interference components. Inthis way, the adaptive signal processing section 14 produces outputsignals with enhanced powers of the desired wave components in thereceived signals with respective delay times (i.e. direct wave, 1-symboldelay wave and 2-symbol delay wave). The three output signals from theadaptive signal processing section 14 are supplied to the path diversitycombiner 15.

[0063] The path diversity combiner 15 effects relative temporal matchingof the received signals with respective delay times, which have beensubjected to the spatial equalization signal processing, by performingtime correction of the 1-symbol delay wave and 2-symbol delay wave withreference to the direct wave. Then, the temporal equalization signalprocessing is effected by synthesizing the resultant signals by anin-phase synthesis method or a maximum ratio synthesis method. The pathdiversity combiner 15 may be replaced with an adaptive equalizer, etc.There is no problem if a temporal equalization processing can beperformed.

[0064] [Re: Transmission Operation]

[0065] The transmission operation will now be described. At the time ofthe transmission, like the above-described reception, the delay profileestimation sections 12-1 to 12-N estimate delay profiles. On the basisof the estimated delay profiles, the DOA estimation section 17 estimatesan arrival angle range of a desired wave. The arrival angle range inthis context means an approximate direction of arrival of desiredsignals, that is, a range of angles at which a desired wave is expectedto come. In this embodiment, in consideration of the directivities ofthe antennas, average received powers of a desired wave in all delayprofiles are simply compared, thereby to estimate the arrival anglerange.

[0066] The delay profiles are indispensable in the temporal/spatialequalization signal processing at the time of reception. Using the delayprofiles, the arrival angle range of a desired wave can be limited tosome degree without performing complex calculations. On the basis of theestimated arrival angle range, the transmission antenna selector 18selects, as transmission antennas, those of the antennas 10-1 to 10-N,which has received the delay waves at maximum power at each delay wave.Based on the information from the transmission antenna selector 18, theswitch 19 is operated and transmission signals are fed to the selectedtransmission antennas.

[0067] An example of a specific operation mode of the present embodimentwill now be described. FIG. 3 shows an example of states of arrivalwaves and delay profiles in a case where radio waves have been receivedby the antennas 10-1 to 10-N. In FIG. 3, a desired wave (direct wave), a1-symbol delay wave, a 2-symbol delay wave, and an interference wave(co-channel interference wave) have arrived at the antennas 10-1 to10-N. Assume that delay profiles of average received powers at intervalsof symbol time T are estimated as shown in FIG. 3.

[0068] As the antennas 10-1 to 10-N, eight directional antennas aredisposed in a circle such that their directivity patterns are directedradially outward from the center of the array. The directivity is acosine beam pattern, and the beam half-value width is 90°. Thus,adjacent beams overlap each other.

[0069] In FIG. 3, only the antennas 10-1, 10-2 and 10-3 receive thedesired wave (direct wave). If the average power delay profiles of theseantennas are compared, the received power value of the antenna 10-1 ishighest. Thus, the switch 19 is controlled by the transmission antennaselector 18, and the antenna 10-1 is used as the transmission antennafor transmitting radio waves.

[0070] In the mobile radio communication system, as mentioned above, thereversibility is established between the uplink (terminal station→basestation) and downlink (base station→terminal station) with respect tothe radio wave arrival direction. Accordingly, if the received powervalue of the antenna 10-1 in the downlink is highest, the terminalstation in the downlink receives the radio wave from the antenna 10-1 asthe wave with the highest received power value. Therefore, if the basestation transmits radio waves via the antenna 10-1 having the highestreceived power value, the reception SNR at the terminal station isenhanced.

[0071] According to the present embodiment, in the mobile radiocommunication system using different frequencies for the uplink anddownlink, too, the radio communication apparatus of the base stationusing the adaptive antenna can easily select optimal antennas and cansend radio waves to the terminal station. Thus, the reception SNR at theterminal station can be enhanced by the diversity effect based ondirectivity diversity.

[0072] Moreover, the arrival angle range of the desired wave can easilybe estimated only by using the delay profiles of the received signals ofthe antennas, which have already been measured for the temporal/spatialequalization processing, and observing the power value of each delaywave. Based on the estimated arrival angle range, the optimaltransmission antennas can be quickly selected with simple processingwith respect to the radio wave arrival direction ensuring reversibilitybetween the uplink and downlink. This embodiment is particularlyeffective in the system requiring high-speed processing, and alsoeffective as a solution to the problem of shadowing.

[0073] (Second Embodiment)

[0074]FIG. 4 shows the structure of a radio communication apparatusaccording to a second embodiment of the invention. The structuralelements common to those in FIG. 2 are denoted by like referencenumerals, and only differences from the first embodiment will bedescribed.

[0075] In the second embodiment, omni-directional antennas 20-1 to 20-Nare substituted for the directional antennas 10-1 to 10-N used in thefirst embodiment. A beam forming section 21 is connected between theantennas 20-1 to 20-N and the duplexers 11-1 to 11-N. The beam formingsection 21 forms a plurality of beams with different directions ofradiation (i.e. different directivities), that is, a plurality ofdirectivity patterns. The beam forming section 21 may be realized, forexample, by a Butler matrix circuit using analog elements, or a digitalcircuit performing spatial FFT (Fast Fourier Transform).

[0076] Since the beam forming section 21 is used, the reception antennaselector 13 in FIG. 2 is replaced with a reception beam selector 22controlled by a control section 23, and the transmission antennaselector 18 in FIG. 2 is replaced with a transmission beam selector 24.The transmission beam selector 24 controls a switch 25.

[0077] [Re: Reception Operation]

[0078] A reception operation of the radio communication apparatusaccording to this embodiment will now be described. The received signalsfrom the antennas 20-1 to 20-N are input to the beam forming section 21,and a plurality of beams with different directions of radiation areformed. The received signals from the beam forming section 21, which areassociated with the respective beams, are input to the reception beamselector 22 via the duplexers 11-1 to 11-N. In parallel with this, thedelay profile estimation sections 12-1 to 12-N estimate average delayprofiles of the associated received signals.

[0079] On the basis of the average delay profiles estimated by the delayprofile estimation sections 12-1 to 12-N, the reception beam selector 22is controlled by a control signal from the control section 23 so as toselect optimal reception beams for desired wave components withassociated delay times. The received signals from the selected receptionbeams are subjected to the spatial equalization processing, such asadaptive array, in the adaptive signal processing section 14, and thento the temporal equalization processing in the path diversity combiner15.

[0080] [Re: Transmission Operation]

[0081] At the time of the transmission, like the above-describedreception, on the basis of the delay profiles estimated by the delayprofile estimation sections 12-1 to 12-N, the DOA estimation section 17estimates an arrival angle range of a desired wave. On the basis of theestimated arrival angle range, the transmission beam selector 24selects, as transmission beams, only those of the beams formed by thebeam forming section 21, which have received the delay waves at maximumpower. Based on the information from the transmission beam selector 24,the switch 25 is operated and transmission signals are fed to the beamforming section 21 so that the transmission signals may be sent out withthe selected transmission beams.

[0082] According to this embodiment, the beam with high SNR is selectedas the reception beam from the plural beams, and the selected beam isused for signal reception. Thus, the reception characteristics at thebase station are improved, and if the same beam is used for atransmission beam, the average reception SNR can be improved at theterminal station.

[0083] (Third Embodiment)

[0084]FIG. 5 shows the structure of a radio communication apparatusaccording to a third embodiment of the invention. This embodiment isbased on the structure of the first embodiment, and it aims at forming atransmission beam pattern capable of effectively enhancing an averagereception SIR at an opposing-side station, or a terminal station.

[0085] The structural elements common to those in FIG. 2 are denoted bylike reference numerals, and only differences from the first embodimentwill be described. In the third embodiment, a direction of arrivalestimation section 27 for estimating a direction of arrival of a desiredwave is provided in addition to the arrival angle range estimationsection 17 for estimating an arrival angle range of a desired wave inthe first and second embodiments. In addition, a transmission weightvector generator 30 is added, and the switch 19 in FIG. 2 is replacedwith weighting sections (multipliers) 31-1 to 31-N.

[0086] [Re: Reception Operation]

[0087] A reception operation in the third embodiment is the same as thatin the first embodiment. The received signals from the antennas 10-1 to10-N are input to the reception antenna selector 13 via the duplexers11-1 to 11-N. In parallel with this, the delay profile estimationsections 12-1 to 12-N estimate delay profiles of the associated receivedsignals.

[0088] On the basis of the delay profiles estimated by the delay profileestimation sections 12-1 to 12-N, the reception antenna selector 13 iscontrolled by the control signal from the control section 16 so as toselect optimal beams for desired wave components with associated delaytimes. The received signals from the selected beams are subjected to thespatial equalization processing, such as adaptive array processing, inthe adaptive signal processing section 14, and then to the temporalequalization processing in the path diversity combiner 15.

[0089] [Re: Transmission Operation]

[0090] At the time of transmission, like the reception, on the basis ofthe delay profiles estimated by the delay profile estimation sections12-1 to 12-N, the arrival angle range estimation section 17 estimates anarrival angle range Φ which is an approximate direction of arrival of adesired wave. Specifically, like the preceding embodiments, the arrivalangle range estimation section 17 first compares desired wave componentpowers in all the delay profiles and finds the arrival angle range Φfrom the directivities of the antennas 10-1 to 10-N.

[0091] Once the arrival angle range Φ is found by the arrival anglerange estimation section 17, the antennas having directivities with nogain in the arrival angle range Φ are regarded as non-associatedantennas, and these are excluded from the candidates by the transmissionantenna selector 18. Thus, the associated transmission antennas areselected.

[0092] Subsequently, in order to improve the precision of estimation ofthe direction of arrival of the desired wave, the direction of arrivalestimation section 27 finds a DOA φ of the desired wave, which is moreprecise than the arrival angle range Φ. This is effected by performing abeam scan and a null pattern scan (to be described later) after thearrival angle range Φ is specified from the comparison of the desiredwave received powers in the delay profiles, as mentioned above.

[0093] Based on the DOA φ estimated by the direction of arrivalestimation section 27, the transmission weight vector generator 30determines transmission weight vectors to direct a maximum gaindirection of the directivity (transmission beam) at the time oftransmission in the direction φ. The weighting sections 31-1 to 31-Nmultiply the transmission signal by these weight vectors. Thus, atransmission signal sequence for the transmission antennas selected bythe transmission antenna selector 18 is generated and sent out with theoptimal transmission beam pattern.

[0094] The transmission beam pattern to be formed will now beconsidered.

[0095] A null pattern is very sensitive to the DOA of received signalssince it causes a gain decrease dynamically relative to the angle. Bycontrast, a main lobe has a relatively large beam width, and a gaindecrease thereof from the peak is gentle relative to the variation inangle. It is thus considered that the main lobe has a high robustness ina case where the estimation precision of DOA is low, a peak error of thebeam occurs due to a defective calibration of the transmission circuit,or the DOA differs between the reception mode and transmission mode dueto movement of the terminal station or a variation in environment.

[0096] Accordingly, it is considered that the transmission beam gain isnot greatly decreased in the direction of arrival (DOA) of the desiredwave, even if the arrival angle range estimation section 17 anddirection of arrival estimation section 27 estimate the DOA φ of thedesired wave by a method with low estimation precision but with a muchless amount of calculations than MUSIC, and the vector generator 30generates transmission weight vectors based on the estimated DOA φ toweight the transmission signal, thereby to form the transmission beampattern.

[0097] Moreover, if a transmission beam pattern, which has very low sidelobes at angles other than the angle of the main lobe in the DOA of thedesired wave, is formed, the radiation gain in the directions ofinterfering stations can be decreased to some extent, if not an optimallevel.

[0098] From the above, it should suffice if the transmission weightvectors are determined so as to form a transmission beam pattern whichhas the beam center (corresponding to the DOA φ) included in the arrivalangle range Φ of the desired wave. This transmission beam pattern shouldhave such a beam width that the radiation gain in the arrival anglerange Φ is a threshold G_(U) [dB] or above, and should have theradiation gain in side lobes which is less than a threshold G_(L) [dB].The thresholds G_(U) and G_(L) are parameters depending on the number ofantennas, antenna directivities, array structure, estimation precisionof power delay profiles, etc. This transmission beam pattern can easilybe obtained, for example, by weighting the Chebyshev distribution towardthe DOA φ of the desired wave.

[0099] How to estimate the DOA (arrival angle range and direction ofarrival) of the desired wave and determine the transmission beam patternbased on the estimated DOA will now be described.

[0100] In the example shown in FIG. 3, only antennas 10-1, 10-2 and 10-8receive desired wave components. If the delay profiles (average delayprofiles) of the respective desired wave components are compared, thereceived power value of the antenna 10-1 is highest, and the receivedpower values of the antennas 10-2 and 10-8 are second highest andsubstantially equal.

[0101] Since the intervals of antennas 10-1 to 10-N are relatively small(about half wavelength), the fading correlation of received signalsamong the antennas 10-1 to 10-N is very high. Thus, the received signalpower values are considered to be substantially equal, and a differencein received power value among the delay profiles occurs due to thedirectivities of antennas 10-1 to 10-N.

[0102] In addition, since the directivity of antennas 10-1 to 10-N issymmetric between the right and left sides, it can be estimated that thedesired wave comes substantially from the front side of the antenna 10-1(assuming φ₀=0°, the angle increasing clockwise) Accordingly, in thiscase, it should suffice if a transmission beam pattern with the centerat φ₀=0° and the beam width at Φ=−11° to 11° is formed.

[0103] Similarly, Φ=45° to 67° with respect to the 1-symbol delay wave,and Φ=124° to 146° with respect to the 2-symbol delay wave. Transmissionbeam patterns with the centers at Φ₁=56° and φ₂=135° and the beam widthat about 22.5° may be formed for the 1-symbol delay wave and 2-symboldelay wave.

[0104] The preciseness of estimation of the arrival angle Φ estimated bythe arrival angle range estimation section 17 depends on the reliabilityof the received power value estimated from the delay profiles. If theeffect of noise is negligible, the arrival angle Φ can be made moreprecise by finding the difference in received power value among theantennas 10-1 to 10-N when the desired wave is received.

[0105] As has been described above, in the third embodiment, like thefirst embodiment, the K (K<N) directional antennas are selected based onthe arrival angle range Φ estimated by the arrival angle rangeestimation section 17. The transmission signal to be supplied to the Kdirectional antennas is weighted by the transmission weight vectors forsetting the maximum gain direction of the transmission beam at thedirection of arrival (DOA) φ of the desired wave, which is estimated bythe direction of arrival estimation section 27. Thereby, thetransmission beam pattern having a high directivity in the maximum gaindirection and having suppressed side lobes can be formed, and theaverage reception SIR at the terminal station can be improved. Moreover,high robustness is provided against a variation in directions of arrivalof the desired wave and interference wave.

[0106] Note that, to determine the transmission weight vectors, outputsof the arrival angle range estimation section 17 and direction ofarrival estimation section 27 are used in the third embodiment. However,to determine the transmission weight vectors, the only output of arrivalangle range estimation section 17 may be used.

[0107] (Fourth Embodiment)

[0108]FIG. 6 shows the structure of a radio communication apparatusaccording to a fourth embodiment of the invention. This embodiment isbased on the structure of the second embodiment. Using the sameprinciple of the third embodiment, the fourth embodiment aims at forminga transmission beam pattern capable of effectively enhancing an averagereception SIR at an opposing-side station, or a terminal station.

[0109] The structural elements common to those in FIG. 4 are denoted bylike reference numerals, and only differences from the second embodimentwill be described. In the fourth embodiment, a direction of arrivalestimation section 27 for estimating a direction of arrival of a desiredwave is provided in addition to the arrival angle range estimationsection 17 for estimating an arrival angle range of a desired wave inthe first and second embodiments. In addition, a transmission weightvector generator 40 is added, and the switch 25 in FIG. 4 is replacedwith weighting sections (multipliers) 41-1 to 41-N.

[0110] [Re: Reception Operation]

[0111] A reception operation of this embodiment is the same as that ofthe second embodiment. The received signals from the antennas 20-1 to20-N are input to the beam forming section 21, and a plurality of beamsare formed. The received signals from the beam forming section 21, whichare associated with the respective beams, are input to the receptionbeam selector 22 via the duplexers 11-1 to 1′-N. In parallel with this,the delay profile estimation sections 12-1 to 12-N estimate averagedelay profiles of the associated received signals.

[0112] On the basis of the delay profiles estimated by the delay profileestimation sections 12-1 to 12-N, the reception beam selector 22 iscontrolled by the control signal from the control section 23 so as toselect optimal reception beams for desired wave components withassociated delay times. The received signals from the selected receptionbeams are subjected to the spatial equalization processing, such asadaptive array processing, in the adaptive signal processing section 14,and then to the temporal equalization processing in the path diversitycombiner 15.

[0113] [Re: Transmission Operation]

[0114] At the time of transmission, like the third embodiment, on thebasis of the delay profiles estimated by the delay profile estimationsections 12-1 to 12-N, the arrival angle range estimation section 17estimates an arrival angle range Φ which is an approximate direction ofarrival of a desired wave. The beams having directivities with no gainin the arrival angle range Φ are excluded from the candidates by thetransmission beam selector 24. Thus, the associated transmission beamsare selected.

[0115] Subsequently, the direction of arrival estimation section 27finds a direction of arrival φ of the desired wave, which is moreprecise than the arrival angle range Φ. Based on the DOA φ, thetransmission weight vector generator 40 determines transmission weightvectors for setting a maximum gain direction of the directivity(transmission beam) at the time of transmission to confirm to thedirection φ. The weighting sections 41-1 to 41-N multiply thetransmission signal by these weight vectors. Thus, a transmission signalsequence for the transmission beam selected by the transmission beamselector 24 is generated and sent out with the optimal transmission beampattern.

[0116] According to this embodiment, the beams with high SNR areselected from the plural beams as the reception beams, and the selectedbeams are used for reception. Thereby, the reception characteristics atthe base station are improved. In addition, the same reception beams areused as transmission beams, and the transmission beams are synthesizedto form an optimal transmission beam pattern. Thus, the averagereception SIR can be further improved at the terminal station.

[0117] Note that, to determine the transmission weight vectors, outputsof the arrival angle range estimation section 17 and direction ofarrival estimation section 27 are used in the third embodiment. However,to determine the transmission weight vectors, the only output of arrivalangle range estimation section 17 may be used.

[0118] (Fifth Embodiment)

[0119] A fifth embodiment of the invention, which relates to a DOAestimation method, will now be described with reference to FIGS. 7A to7F.

[0120] In the present invention, where a sufficient angular resolutionis not obtained with the above-described DOA estimation method, a beampattern scan or a null pattern scan may be used as a DOA estimationmethod with a less amount of calculations, which is a substitute for theMUSIC.

[0121] According to the DOA estimation using the beam pattern scan, aweighting corresponding to an angular sweep is attempted for receivedsignals and thus a more exact DOA can be estimated. For example, in thefirst and third embodiments using the directional antennas 10-1 to 10-N,some antennas having high gains in the arrival direction can bespecified from the delay profiles of received signals from thedirectional antennas 10-1 to 10-N. Thus, two of those antennas, whichhave the highest received powers, may be used to form a scanning beampattern. In the example shown in FIG. 3, with respect to the desiredwave, a scanning beam pattern is produced using the antennas 10-1 and10-2.

[0122] Based on this scanning beam pattern, an angular sweep isperformed. That is, a beam scan is performed at proper angular intervalswithin the initially estimated arrival angle range Φ. As a result of thescan using the scanning beam pattern, the direction in which thereception output level corresponding to the scanning beam pattern takesa maximum value is estimated to be the arrival direction φ of thedesired wave. If the angular scan is performed too finely, theprocessing time and the amount of calculations become two large. It isthus preferable to discretely perform the angular sweep at such angularintervals as to make negligible the gain degradation from the peak inrelation to the width of the main lobe of the scanning beam pattern.

[0123] Normally, if the above beam pattern scan is performed in ahorizontal plane over 360°, distinction between the side lobe, gratinglobe, etc. is difficult. In this invention, however, the estimatedreception wave arrival direction Φ is limited in advance. Thus, the scanrange can be narrowed and the desired wave direction can be exactlyestimated by a less number of attempts.

[0124]FIGS. 7A and 7B show states in which the estimation of thedirection is performed using the beam pattern scan. FIG. 7A shows ascanning beam pattern formed by using two antennas. FIG. 7B shows ahysteresis of the reception output level (the synthesis output of twoantennas) obtained where this scanning beam pattern is angular-sweptover the arrival angle range Φ. From FIG. 7B, the desired wave arrivaldirection φ₀ is found as an angle at which the reception output leveltakes a maximum value.

[0125] In this way, the arrival direction φ can be estimated by simplearithmetic operations, the arrival direction φ can be made to completelycoincide with the maximum gain direction (peak direction) of thetransmission beam, and the maximum SNR is realized at the terminalstation.

[0126] It is also possible to apply an angular sweep method wherein ascanning null pattern having a null is formed by using two antennas, asshown in FIG. 7C. In this case, a hysteresis of the reception outputlevel (the synthesis output of two antennas) corresponding to thescanning null pattern is shown in FIG. 7D. The angle at which thereception output level takes a minimum value is estimated as the desiredwave arrival direction φ₀.

[0127] If the scan is performed using the scanning null pattern, theminimum value can easily be specified since the null drops steeply evenin such a case that there would be no difference in reception outputlevel due to the scanning beam width in the beam pattern scanning andthe arrival direction cannot be specified. Thus, the desired wavearrival direction φ₀ can easily be estimated.

[0128] Moreover, the above-described beam pattern scan and null patternscan may be performed simultaneously, as illustrated in FIG. 7E. Adifference between reception output levels corresponding to the twopatterns is found, as shown in FIG. 7F, and the angle at which thedifference is greatest is estimated as the desired wave arrivaldirection φ₀.

[0129] With this technique, the arrival direction can be estimated moreprecisely since the effect of noise, delay wave, interference wave, etc.is suppressed. Furthermore, since this method is equivalent to the casewhere the above-described arrival angle range Φ of the desired wave isexcessively decreased, a narrow beam with a higher gain at the beamcenter of the beam pattern can be formed.

[0130] If the angular sweep is always performed from the end firedirection of the directional antenna, there may arise a case where muchtime is needed to obtain a minimum value in reception output level.However, if the minimum value search according to a two-division methodis repeatedly attempted, the desired wave arrival direction can beestimated more quickly with a less amount of calculations.

[0131] (Sixth Embodiment)

[0132] A sixth embodiment of the invention, which relates to a DOAestimation method different from that of the fifth embodiment, will nowbe described with reference to FIG. 8. The method to be described belowis applicable to all the arrival angle range estimation sections 17 anddirection of arrival estimation section 27 of the radio communicationapparatuses according to the first to fourth embodiments. Assume,however, that the method is applied to the radio communication apparatusaccording to the third embodiment as shown in FIG. 5.

[0133] In the DOA estimation method described in connection with thefifth embodiment, there is a case where the DOA cannot exactly beestimated when high-level delay waves come from the vicinity of thedirection of the desired wave. In such a case, replicas of receivedsignals, wherein propagation channel responses (complex amplitude phasedistortion components) due to the desired arrival wave are convoluted,are generated from the delay profile estimation values of the twoantenna elements covering the estimated arrival direction range. Thegenerated replica of received signals are subjected to the null patternscan, etc. which is the arrival direction estimation method described inthe fifth embodiment. Thereby, the error in DOA estimation of thedesired wave and delay waves can be reduced.

[0134]FIG. 8 shows the structure of the DOA estimation section of theradio communication apparatus according to the sixth embodiment of theinvention.

[0135] The operational principle will now be described with reference toFIG. 8. In FIG. 8, #1 and #2 denote two elements having higher receivedpowers of delay waves with a delay time τ_(i). Two received signals areinput to the delay profile estimation sections 12-1 and 12-2, and delayprofiles are estimated. Based on the delay profiles, replica generators50-1 and 50-2 generate reception replica signals of delay waves to bedesired.

[0136] Then, the arrival direction is estimated from the receptionreplica signals of the two elements by a null pattern scanner 51. Theexact scan determination can be made by performing the null pattern scanusing the reception replica signals containing only the specific delaywave components. In FIG. 8, the null pattern scanner may be replacedwith a beam pattern scanner.

[0137] The replica of received signals can be generated for the desiredwave and each delay wave, according to the following principle. Areceived signal x_(j)(t) of a j-th antenna element is given by$\begin{matrix}{{x_{j}(t)} = {{\sum\limits_{i = 1}^{L}{{h_{j}(t)}{s\left( {t - \tau_{i}} \right)}}} + {n(t)}}} & (4)\end{matrix}$

[0138] wherein h_(j)(t) indicates a propagation path response containingan array response in the j-th antenna element, τ_(i) is a delay time(I=1 to L) of an I-th delay wave, s(t) is a transmission signal sequence(PN sequence), and n(t) is noise in the receiver.

[0139] If a complex conjugate of a known sequence, which is the same asthat of the transmission signal, is convoluted in the received signal inorder to find a delay profile, the following is given: $\begin{matrix}{{\int_{- \infty}^{\infty}{{x_{j}(t)}{s^{*}\left( {\tau - t} \right)}{\quad \tau}}} = {\sum\limits_{i = 1}^{L}{{{\hat{h}}_{j}(t)}{\delta \left( {t - \tau_{i}} \right)}}}} & (5)\end{matrix}$

[0140] wherein h{circumflex over ( )}_(j)(t) is an estimated complexdelay profile.

[0141] Therefore, the reception replica signal of the i-th delay wave ofthe j-th antenna element is found by

r _(i,j)(t)=ĥ _(j)(t)s(t−τ _(i))  (6)

[0142] With the above structure, the error of DOA estimation using thenull pattern scan can be reduced.

[0143] Where the transmission beam is formed using the transmissionweight vectors for setting the null in the estimated delay wavedirection, the delay component reaching the terminal can be reduced.Thereby, frequency selective fading at the terminal can be prevented. Asa weight vector determination algorithm for thus directing the null,there is known, for instance, a DCMP (Directional Constraint MinimumPower) algorithm with which a desired beam pattern is obtained byimposing a constraint to the known arrival direction.

[0144] (Seventh Embodiment)

[0145] A seventh embodiment of the invention, which relates to a DOAestimation method different from that of the fifth embodiment, will nowbe described with reference to FIG. 9.

[0146] With the DOA estimation method described in connection with thefifth and sixth embodiments, there is a case where the DOA cannotexactly be estimated when incoming high-level interference waves varyover time in a communication system using an access method such as SDMA(Space Division Multiple Access) or CDMA (Code Division MultipleAccess).

[0147] A DOA estimation method applicable to a case where high-levelinterference waves are present will now be described.

[0148] The operational principle will now be described with reference toFIG. 9. An N-number of received signals from respective antenna elementsare input to the delay profile estimation sections 12-1 to 12-N, anddelay profiles are estimated. Based on the delay profiles, replicagenerators 60-1 to 60-N generate reception replica signals of thedesired wave and all delay waves. The reception replica signals of thedesired wave and each delay wave are generated by the same method asdescribed above.

[0149] The reception replica signals of the desired wave and all delaywaves are synthesized and subtracted from the received signals by theadders 52-1 to 52-N. Thus, received signals containing the interferencewave components alone are obtained.

[0150] A null pattern scanner 61 estimates the interference wave arrivaldirection with respect to all combinations of adjacent two of theantenna elements associated with the N received signals. When theinterference wave arrival direction is to be estimated, if it issufficient to find the arrival direction of interference waves onlywithin the desired wave arrival angle range, the interference wavearrival direction may be estimated using the antenna within the desiredwave arrival angle range.

[0151] With the above method, the interference wave direction isestimated. In addition, if the transmission beam pattern for setting thenull in the estimated interference wave direction is formed, thereception SIR at the terminal station can be improved in thecommunication system, such as SDMA or CDMA, where many high-levelinterference-waves are present. Moreover, in an inter-base-stationasynchronous system, an inter-base-station interference can be reduced.

[0152] (Eighth Embodiment)

[0153] According to the radio communication apparatus according to theseventh embodiment, the transmission beam pattern for setting the nullin the interference wave arrival direction can be formed. However, thetransmission beam cannot be directed to the desired wave arrivaldirection.

[0154] In a radio communication apparatus according to the eighthembodiment, the function of the radio communication apparatus of thesixth embodiment is combined with the function of the radiocommunication apparatus of the seventh embodiment. Thereby, thetransmission beam can be directed to the desired wave and the null canbe directed to the interference wave.

[0155]FIG. 10 shows the structure of a DOA estimation section of theradio communication apparatus according to the eighth embodiment of theinvention. The structural elements common to those in FIGS. 8 and 9 aredenoted by like reference numerals.

[0156] In FIG. 10, the replica generators 50-1 to 50-N for a desiredwave and the null pattern scanner 51 for a desired wave find the delaywave (desired wave) arrival direction, as described in connection withthe sixth embodiment. The found delay wave (desired wave) arrivaldirection is input to the transmission weight vector generator 30.

[0157] On the other hand, the replica generators 60-1 to 60-N, adders52-1 to 52-N and null pattern scanner 61 for interference waves find theinterference wave arrival direction, as described in connection with theseventh embodiment. The found interference wave arrival direction isinput to the transmission weight vector generator 30.

[0158] Based on the delay wave (desired wave) arrival direction outputfrom the null pattern scanner 51 for desired wave and the interferencewave arrival direction output from the null pattern scanner 61 forinterference waves, the transmission weight vector generator 30generates such transmission weight vectors as to direct the null to theinterference wave arrival direction and to provide a maximum gain to thedirectivity in the delay wave (desired wave) arrival direction.

[0159] According to the radio communication apparatus of the eighthembodiment, the transmission beam having both the advantages of theradio communication apparatuses of the sixth and seventh embodiments canbe obtained. That is, the null can be directed to the interference wavearrival direction, and the directivity for transmission has a maximumgain in the delay wave (desired wave) arrival direction.

[0160] The embodiments of the present invention have been described, butvarious modifications may be made as will be stated below.

[0161] (1) If the terminal station has means, such as a RAKE receiver oran adaptive equalizer, for separating a received signal of a desiredwave and a received signal of delay waves of the desired wave and thensynthesizing them through delaying operation, weighting, etc., thearrival angle range and arrival direction of not only the desired wavebut also the delay wave may be estimated. Thus, a transmission beamhaving a gain in both the desired wave arrival direction and the delaywave arrival direction may be formed, or a multi-beam for the desiredwave and delay wave may be formed. Thereby, a transmission diversityeffect is obtained.

[0162] (2) In the preceding embodiments, the FDD system having differentfrequencies for transmission and reception is assumed. However, thepresent invention is applicable to the TDD system, as mentioned above.In this case, if the duplexer, 11-1 to 11-N, is replaced with acirculator having bi-directional isolation for three terminals, the sameconstruction is realized and the same advantages are obtained.

[0163] (3) In the preceding embodiments, the system having no feedbacksignals from the terminal station to the base station is assumed as thesystem to which the present invention is applicable. However, iffeedback signals from the terminal are available, a transmission beamcontrol for maximizing the average reception SIR at each terminalstation can be performed in the base station.

[0164] As has been described above, the present invention can provide aradio communication apparatus using an adaptive antenna, wherein theamount of arithmetic operations necessary for the arrival directionestimation and transmission weight vector determination, which in theprior art require a great deal of calculations and complex processes,can be remarkably reduced, and a transmission beam having robustness toa variation in arrival direction can be formed. Thereby, the averagereception SNR and average reception SIR at the opposing-side station canbe improved. Accordingly, the repetition distance of the same frequencycan be decreased, and as a result the frequency use efficiency of thesystem can be improved.

[0165] The present invention is applicable to a system using differentfrequencies for uplink and downlink. Thus, even in FDD-side system, theaverage reception SIR at the opposing station can be improved by thetransmission beam control.

[0166] In the case that the radio communication apparatus of thisinvention is applied to currently employed cellular system basestations, the received signal strength at the terminal station isenhanced by the directivity gain of the transmission beam andconsequently high-quality communication is ensured.

[0167] Furthermore, it is considered that with the directivity gain ofthe transmission beam, the coverage of cells increases equivalently.Thereby, non-sensitive zones can be eliminated, and the number ofhandover controls can be reduced.

[0168] Additional advantages and modifications will readily occur tothose skilled in the art. Therefore, the invention in its broaderaspects is not limited to the specific details and representativeembodiments shown and described herein. Accordingly, variousmodifications may be made without departing from the spirit or scope ofthe general inventive concept as defined by the appended claims andtheir equivalents.

1. A radio communication apparatus comprising: a plurality ofdirectional antennas; a delay profile estimation section configured toestimate a delay profile representing arrival times of a desired waveand delay waves and received powers for each of received signals fromsaid antennas; an arrival angle range estimation section configured toestimate an arrival angle range of said desired wave from the delayprofiles of the received signals estimated by said delay profileestimation section; a transmission antenna selection section configuredto select at least one of the antennas which is to be used fortransmission, on the basis of the arrival angle range estimated by saidarrival angle range estimation section; a transmission sectionconfigured to transmit transmission signals using said at least oneantenna selected by said transmission antenna selection section; and areception antenna selection section configured to select at least one ofthe antennas which is to be used for reception, on the basis of thearrival angle range estimated by said arrival angle range estimationsection.
 2. A radio communication apparatus according to claim 1,further comprising: a transmission weight vector generating sectionconfigured to generate transmission weight vectors so as to set amaximum gain direction of directivity at a time of transmission in thearrival angle range estimated by the arrival angle range estimationsection, wherein said transmission antenna selection section selects aplurality of antennas included in the arrival angle range estimated bythe arrival angle range estimation section, and said transmissionsection feeds to the antennas selected by the transmission antennaselection section transmission signals multiplied by the transmissionweight vectors generated by the transmission weight vector generatingsection, thereby transmitting the transmission signals.
 3. A radiocommunication apparatus according to claim 2, further comprising: anarrival direction estimation section configured to estimate a directionof arrival of the desired wave from the arrival angle range estimated bysaid arrival angle range estimation section, wherein the transmissionweight vector generating section generates the transmission weightvectors so as to set the maximum gain direction of the directivity atthe time transmission in the arrival direction estimated by the arrivaldirection estimation section.
 4. A radio communication apparatusaccording to claim 3, wherein said arrival direction estimation sectioncomprises a section configured to detect the arrival direction byperforming a scan using a predetermined scanning beam pattern within thearrival angle range estimated by said arrival angle range estimationsection, and finding a maximum value of a reception output levelobtained by said scan.
 5. A radio communication apparatus according toclaim 3, wherein said arrival direction estimation section detects thearrival direction by performing a scan using a predetermined scanningnull pattern within the arrival angle range estimated by said arrivalangle range estimation section, and finding a minimum value of areception output level obtained by said scan.
 6. A radio communicationapparatus according to claim 3, wherein said arrival directionestimation section comprises a section configured to detect the arrivaldirection by performing a scan using a predetermined scanning beampattern and a scan using a predetermined scanning null pattern withinthe arrival angle range estimated by said arrival angle range estimationsection, and finding a maximum value in difference between receptionoutput levels obtained by said both scans. 7-20. (Canceled).